The present invention generally relates to vehicle brakes and more particularly relates to an actuating unit for an electromechanically operable disc brake for automotive vehicles which is arranged on a brake caliper.
An electromechanical actuating unit of this general type is disclosed in DE 195 11 287 A1. In the actuating unit known in the art, the electric motor, by the intermediary of a planetary gear, drives the thread nut of a roller-and-thread drive whose threaded spindle actuates the first friction lining. The rotor of the electric motor additionally serves as the sun wheel of the planetary gearing, whose planet pinions are mounted in the thread nut and cooperate with a hollow wheel designed in the brake caliper. By way of the thread nut, the rotor is supported in a central bearing arranged in the brake caliper.
The state of the art actuating unit has disadvantages inasmuch as, during its actuation, disturbances which are due to the clamping force of the electromechanical brake and also the transverse forces and bending moments which occur during operation are transmitted via the roller-and-thread drive to the rotor so that it is impossible to guarantee the presence of a constant air gap between the stator and the rotor. This impairs the rate of efficiency of the above-mentioned arrangement. Further, the rotor which is used as the sun wheel of the planetary gearing may become damaged by the effect of the above-mentioned forces or bending moments which may lead to an inclined positioning in relation to the stator.
Therefore, an object of the present invention is to improve upon an electromechanic actuating unit of the type initially referred to in such a manner that the second reduction gear is uncoupled from the first reduction gear so that an equal position of the rotor relative to the planet pinions as well as of the planet pinions relative to the hollow wheel can be ensured.
According to the present invention, this object is achieved in that the electric motor, the first reduction gear, and the second reduction gear are configured as at least two assemblies which can be handled independently, so that the electric motor is arranged outside of the flux of force of the clamping force and its operation cannot be impaired by interferences.
To specify the idea of the present invention, the electric motor, the first reduction gear, and the second reduction gear are configured as each one assembly which can be handled independently. An electromechanic actuating unit of such a construction is distinguished by a high rate of efficiency, an extraordinary dynamics of brake actuation, and an extremely compact type of construction permitting the transmission of high mass-related brake torques. Further, the modular-design assemblies can be manufactured and tested separately.
In a favorable improvement of the object of the present invention, the second reduction gear is arranged on the side of the electric motor remote from the brake linings. This measure permits uncoupling the second reduction gear from the first reduction gear in terms of construction so that deformation of the second reduction gear is reliably prevented and constant clearances may be maintained within the gear.
In another favorable embodiment of this invention, a short force transmission travel of the clamping force is achieved because the first reduction gear is configured as a roll-body and thread drive whose thread nut cooperates with the second reduction gear.
Alternatively, the first reduction gear can be designed as a roll-body and thread drive whose threaded spindle cooperates with the second reduction gear. This measure achieves optimizing the central bearing which cooperates with the threaded spindle.
In another favorable aspect of the present invention, the first reduction gear is configured as a roller-and-thread drive, preferably a roller-and-thread drive with an inward roller return arrangement. Optimal force transmission can be achieved due to the high load capacities of the thread rollers, and the inward return arrangement of the thread rollers permits an easy manufacture of the thread nut.
In another embodiment of the present invention which distinguishes particularly by a low sensitivity to transverse forces, the first reduction gear is configured as a ball-and-thread drive.
In this arrangement, it is especially advantageous that the actuating element is in a force-transmitting connection with the threaded spindle of the roll-body and thread drive and is formed of a force transmission plate which is guided in an annular housing in which the roll-body and thread drive is incorporated. Preferably, the force transmission plate includes at least two radially opposite guiding pins which are accommodated by correspondingly designed guiding surfaces in the housing. These measures permit achieving an effective isolation of the clamping force from the transverse forces which occur during operation and are introduced into the brake caliper.
In another favorable embodiment of the present invention, the thread nut is axially supported on a bearing ring arranged in the housing, and a force sensor is arranged between the bearing ring and the housing. These measures permit realizing a concept with a very short flux of force, with the force sensor representing a component which is arranged in the flux of force, yet is not entrained in movement.
In still another favorable aspect of the present invention, a favorable distribution of load in the ball-and-thread drive is achieved by a conical bore incorporated in the threaded spindle of the ball-and-thread drive in which a push rod is received which serves to transmit pressure forces and the ends of which are supported in an axial extension of the force transmission plate or on the bottom of the bore in a rotationally fixed manner. The threaded spindle is only tensilely loaded due to these measures, and the load portions of the indivdiual balls are rendered more uniform.
To effectively protect the actuating mechanism, especially against contaminants, for example splash water, an elastic seal is provided between the force transmission plate and the housing in another advantageous aspect of the present invention.
In order to considerably reduce the necessary drive torque to be generated by the electric motor, the second reduction gear is configured as a planetary gearing. The planetary gearing is a non-friction gear in which shape variation is not needed and by which high efficiency in little mounting space can be reached.
A higher gear ratio is achieved in another embodiment of the object of the present invention in that the second reduction gear is designed as a planetary gearing with stepped planet pinions.
The attainable gear ratio can be increased further in that the planet pinions with their first step are in engagement with a sun wheel, while the planet pinions with their second step are in engagement with a hollow wheel, by the intermediary of each one spur wheel. However, it is also easily possible to design the second reduction gear as a two-step differential planetary gearing. In the latter type of gearing, an optimal overall length is achieved by using a larger sun wheel.
In another favorable aspect of the object of the present invention, mounting space is optimized because the sun wheel of the planetary gearing is designed on the rotor, while the planet pinions are mounted in a pinion cage that is in a force-transmitting connection with the thread nut. The planet pinions are comprised of each one first large-diameter planet pinion that is in engagement with the sun wheel and each one smaller-diameter second planet pinion that is in engagement with a hollow wheel. The hollow wheel of the planetary gearing is preferably formed of an internally toothed outer ring of a radial bearing in which the pinion cage is supported. These measures achieve a high degree of integration of the arrangement.
The transverse forces which occur during operation are effectively uncoupled in another preferred aspect of the present invention because the actuating element is the thread nut of the roll-body and thread drive.
Uncoupling of the flux of force from the drive unit or the electric motor is ensured according to another feature of the present invention in that there is provision of a guiding element that embraces the thread nut and is supported on an annular housing receiving the roll-body and thread drive. The threaded spindle is axially supported on the guiding element. The axial support of the threaded spindle is effected by means of a radial bead by the intermediary of an axial bearing. This renders it possible to use a bearing with a very small diameter.
Further, it is especially favorable that force-measuring elements are arranged on the guiding element so that force measurements can be performed on the part that is not entrained in movement and subjected to a defined deformation.
An effective protection of the arrangement against contaminants and the ingress of water is reached by an elastic seal or gasket that is interposed between the thread nut and the guiding element.
A direct introduction of the transverse forces which occur during operation into the housing of the first reduction gear is effected in that the thread nut on its end close to the first friction lining is guided in a guiding ring. In order to effectively protect also this arrangement against the ingress of contaminants, e.g. splash water, an elastic seal or gasket is provided between the thread nut and the guiding ring.
In another favorable embodiment of the object of the present invention, the sun wheel of the planetary gearing is provided on the rotor, while the planet pinions are mounted in a pinion cage that is in a force-transmitting connection with the threaded spindle and are comprised of a first large-diameter planet pinion that is in engagement with the sun wheel and a second smaller-diameter planet pinion that is in engagement with a hollow wheel.
In the above-mentioned embodiment, the mounting space is optimized in that the hollow wheel of the planetary gearing is formed of an internal toothing which is provided in a cover that represents a casing of the planetary gearing and is arranged on the housing of the electric motor.
The assembly of the actuating unit of the present invention is considerably simplified in another embodiment of the object of the present invention in that the force is transmitted between the pinion cage and the threaded spindle by means of a form-locking plug coupling.
In a low-cost design of the actuating unit of the present invention, the pinion cage is mounted in the cover by means of a radial bearing. A planetary gearing of this type is easy to manufacture and can be tested separately.
It is expedient when the form-locking plug coupling is coupled to the pinion cage in a torsionally resistant, radially yielding and flexible manner. This measure ensures an effective isolation from interferences.
The threaded spindle may preferably have a one-part or multi-part design.
Another favorable embodiment of the object of the present invention is characterized in that the thread nut at its end remote from the first friction lining includes an axial projection which is movable into abutment on a stop that is designed on the threaded spindle also in an axial direction and acts in a circumferential direction. It is achieved by this measure that in particular in a faulty release action, where the thread nut is turned backwards until its stop, the first reduction gear will not be twisted or jammed.
In order to simultaneously fulfil a parking brake function with the actuating unit of the present invention, it is proposed that electromechanical means be provided which allow mechanically locking the rotor of the electric motor.
In a particularly fail-safe design which is based on the form-lock principle, the means is formed of a toothed rim connected to the rotor and an electromagnetically operable lock pawl.
The lock pawl preferably includes catching means which permit locking engagement both in the actuated and the non-actuated position.
In further favorable embodiments of the present invention, the electric motor may be configured as an electronically commutated electric motor energized by a permanent magnet (direct-current motor without brushes) or as a switch reluctance motor (SR motor).
The mentioned types of motors are especially suitable for producing high torques during standstill.
In order to electronically commutate the motor of the actuating unit it is required to arrange for a position detection system which renders possible to detect the position of the rotor of the electric motor relative to the stator and preferably includes a Hall sensor or a magnetoresistive element.
The present invention will be explained in detail in the following description of three embodiments by making reference to the accompanying drawings.